c1 = conv([1 0],[1 2]);
c2 = conv(c1, [1 3]);
c = conv(c2, [1 100]);

cd = polyder(c);
r = roots(cd);

sig = 1/4*(0 - 2 - 3 - 100);

K = polyval(c,r(2));

H = tf(1,c);
rlocus(-H);